Scanning electron microscopes are known in the art. U.S. Pat. No. 5,659,172 of Wagner describes a method for reliable defect detection using multiple perspective Scanning Electron Microscope (SEM) images.
A SEM usually includes an electron gun for generating an electron beam, a SEM lens system for focusing and converging the electron beam, a deflection coil for deflecting the electron beam, a detector for detecting electrons, such as secondary emitted electron or reflected electrons that are emitted/reflected from an inspected object and a processor that is operative to construct SEM images in response to detection signals provided from the detector.
Usually, the electron gun, the SEM lens system and the deflection coil are located within a column that is commonly referred to as SEM column. Focused ion beam (FIB) systems are known in the art. FIB systems are generally utilized to perform milling of small areas within a die, and cross sectioning. The milled or cross-sectioned area is usually analyzed to inspect pattern profiles and to detect defects. FIB systems can also be utilized to generate FIB images.
FIB systems usually include an ion source for generating an ion beam, a FIB lens system for focusing the ion beam to provide a focused ion beam and an ion beam deflector for deflecting the focused ion beam. Typically, a broad ion beam is utilized for an initial milling step, while a narrower ion beam is utilized for a successive step of polishing the walls of the cross sectioned wafer.
A FIB system that is operative to generate a FIB image also has a detector and a processor. Usually, the ion source, the FIB lens system and the ion beam deflector are located within a column that is commonly referred to as FIB column. The detector can also be placed within the FIB column.
Systems that include both FIB and SEM systems are known in the art and are referred to as FIB/SEM systems. Such a system is the XL860 DualBeam Workstation of FEI.
A common FIB ion source generates Gallium ion beams. When a focused Gallium ion beam is directed towards an area at the surface of an integrated circuit it removes a portion of that area to form a cavity defined by cavity defining walls. The Gallium ion beam also contaminates that integrated circuit, as illustrated by “Defects and Gallium—Contamination During Focused Ion Beam Micro Machining”, By C. Leher, L. Frey, S. Peterson, M. Mizutani, H. Ryssel, and “Implemented gallium-ion concentrations of focused-ion beam prepared cross sections”, T. Ishitani and others, 1907 Journal of Vacuum Science Technology, B 16(a), July/August 1998.
Some prior art methods suggest a reduction of ion contamination during the processing steps of a semiconductor. U.S. Pat. Nos. 5,306,945 and 6,114,222 are believed to provide an adequate description of the state of the art.
U.S. Pat. No. 5,306,945 of Drummond suggests to reduce ion contamination by providing an integrated circuit that includes a barrier for terminating the edge of a semiconductor die. The barrier reduces contamination of the dielectric layers such as TEOS and BPSG from mobile ions which are inherent in fabrication materials. While the barrier can be formed at many points in the die fabrication process, its formation is preferably incorporated into the Metal1 mask.
U.S. Pat. No. 6,114,222 of Thakur describes a method for reducing ion contamination. The method includes forming active field effect transistors in a starting substrate; forming a first insulating layer over the field effect transistor and the field oxide; forming a second insulating layer over the first insulating layer; and performing an annealing step in a nitrogen containing gas ambient prior to exposing the insulating layer to mobile ion impurities. Thakur further suggests another method to cure mobile ion contamination during semiconductor processing by annealing an insulating layer in a nitrogen containing gas ambient prior to exposing said insulating layer to mobile ion impurities.